Conversion circuit and electronic circuit

Abstract

This conversion circuit converts an input current into an output voltage, and comprises: a first terminal that is an input section for the input voltage; a second terminal that is a ground; a third terminal that is an output section for the output voltage, and is for supplying a power source voltage via a power source supply resistor; a first resistor that is connected to the first terminal at one end and is connected to the third terminal and the other end; and a regulator that detects the difference between the voltage of the first terminal and a preset reference voltage, and when the voltage of the first terminal is higher than the reference voltage, performs control so as to adjust, in accordance with said difference, the quantity of current flowing from the third terminal to the second terminal, lower the voltage of the third terminal, and maintain the voltage of the first terminal at the reference voltage, wherein the gain of the conversion circuit is determined by the first resistor.

Description

[Technical field]

[0001] The present invention relates to a conversion circuit and an electronic circuit. [Background technology]

[0002] Examples of circuits and elements that use a power supply include condenser microphone units and sensors. For example, condenser microphones are generally integrated with FETs (Field effect transistors) or use external FETs. For this reason, when using a condenser microphone, it is necessary to supply a power supply voltage to the FET.

[0003] FIG. 15 is a diagram showing a microphone circuit and an example of an input / output signal in a conventional technique. When the microphone mic is a condenser microphone, as shown in FIG. L The power supply voltage Vcc is supplied via the microphone mic. The microphone mic includes a FET. The incoming signal (symbol g902) picked up by the microphone mic is O If the fluctuation in the current flowing through the microphone mic is ΔImic and the fluctuation in the power supply voltage Vcc due to noise is ΔVcc, the voltage fluctuation ΔVout of the output signal output from the output terminal Vout is ΔVcc-R L × ΔImic. When there is noise (symbol g901) on the power supply, ΔVout has a term ΔVcc as shown here, so the power supply noise is superimposed on the output signal (symbol g903).

[0004] In order to deal with such noise superimposed on the output of a condenser microphone, a configuration has been proposed in which an operational amplifier is used to apply the noise components superimposed on the power supply voltage Vcc due to capacitive coupling with the internal power supply wiring to the non-inverting input terminal of the operational amplifier, thereby canceling the noise components with the operational amplifier (see, for example, Patent Document 1).

[0005] The fundamental background behind the proposal of circuit configurations that cancel such noise components is not only the fact that power supply noise is easily superimposed on signals, but also the fact that sensors and electronic circuits (e.g., amplifier circuits) tend to be installed far apart. For example, when an amplifier circuit is installed near a sensor, a stable power supply for the amplifier circuit may be required in addition to the weak voltage applied to the sensor. As a result, the sensor and electronic circuit are installed far apart, and external noise such as power supply noise and transmission line noise is superimposed on the signal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-245729 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology described in Patent Document 1 requires many external circuit components for the microphone or microphone unit. Also, the circuit described in Patent Document 1 is a circuit dedicated to condenser microphones, and it is difficult to apply it to other elements, such as sensors.

[0008] The present invention has been made in consideration of the above problems, and has an object to provide a conversion circuit and an electronic circuit capable of reducing the superimposition of noise. [Means for solving the problem]

[0009] (1) In order to achieve the above object, a conversion circuit according to one embodiment of the present invention is a conversion circuit that converts an input current into an output voltage, comprising: a first terminal which is an input part for the input current; a second terminal which is ground; a third terminal which is a power supply part for the conversion circuit and an output part for the output voltage; a first resistor having one end connected to the first terminal and the other end connected to the third terminal; and a regulator that detects a difference between a voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts an amount of current flowing from the third terminal to the second terminal in accordance with the magnitude of the difference, thereby controlling so as to maintain the voltage of the first terminal at the reference voltage, wherein a gain is determined by the first resistor.

[0010] (2) Also, in the conversion circuit described above in (1), the current flowing from the third terminal to the second terminal may be a sink current, and the sink current may be supplied to the third terminal from outside the conversion circuit.

[0011] (3) In the circuit of (1) or (2) above, the regulator may include a variable shunt regulator, a reference terminal of the variable shunt regulator being connected to the first terminal, an anode terminal of the variable shunt regulator being connected to the second terminal, and a cathode terminal of the variable shunt regulator being connected to the third terminal.

[0012] (4) Also, in the conversion circuit of (1) or (2) above, the regulator may include an operational amplifier and a first NPN transistor, a positive input terminal of the operational amplifier being connected to the first terminal, a negative input terminal of the operational amplifier receiving the reference voltage, an output terminal of the operational amplifier being connected to a base of the first transistor, a collector of the first transistor being connected to the third terminal, and an emitter of the first transistor being connected to the second terminal.

[0013] (5) Also, in the conversion circuit of (1) or (2) above, the regulator may include a first NPN transistor, a second NPN transistor, and a second resistor, wherein the base of the first transistor is connected to the first terminal, the emitter of the first transistor is connected to the second terminal via the second resistor, the emitter of the first transistor is connected to the base of the second transistor, the collector of the first transistor is connected to the collector of the second transistor, the collector of the second transistor is connected to the third terminal, and the emitter of the second transistor is connected to the second terminal.

[0014] (6) In the conversion circuit of (1) or (2), the regulator includes a first NPN transistor, a second NPN transistor, a third PNP transistor, a fourth NPN transistor, a second resistor, a third resistor, and a fourth resistor, the base of the first transistor is connected to the first terminal, the emitter of the first transistor is connected to the second terminal via the second resistor, the emitter of the first transistor is connected to the base of the second transistor, the collector of the first transistor is connected to the third terminal, and the emitter of the second transistor is connected to the base of the second transistor. a collector of the second transistor connected to the third terminal via the third resistor, a collector of the second transistor connected to the base of the third transistor, an emitter of the third transistor connected to the third terminal, a collector of the third transistor connected to the base of the fourth transistor, a collector of the third transistor connected to the second terminal via the fourth resistor, a collector of the fourth transistor connected to the third terminal, and an emitter of the fourth transistor connected to the second terminal.

[0015] (7) In the conversion circuit of (1) or (2), the regulator may include a first NPN transistor, a second NPN transistor, a third PNP transistor, a second resistor, and a third resistor, wherein the base of the first transistor is connected to the first terminal, the emitter of the first transistor is connected to the second terminal via the second resistor, the emitter of the first transistor is connected to the base of the second transistor, the collector of the first transistor is connected to the third terminal, the emitter of the second transistor is connected to the second terminal, the collector of the second transistor is connected to the third terminal via the third resistor, the collector of the second transistor is connected to the base of the third transistor, the emitter of the third transistor is connected to the third terminal, and the collector of the third transistor is connected to the second terminal.

[0016] (8) Also, in the conversion circuit of (1) or (2) above, the regulator may include a first field effect transistor, a second field effect transistor, and a second resistor, wherein the gate of the first field effect transistor is connected to the first terminal, the source of the first field effect transistor is connected to the second terminal via the second resistor, the source of the first field effect transistor is connected to the gate of the second field effect transistor, the drain of the first field effect transistor is connected to the drain of the second field effect transistor, the drain of the second field effect transistor is connected to the third terminal, and the source of the second field effect transistor is connected to the second terminal.

[0017] (9) Also, in the conversion circuit of (1) or (2) above, the regulator may include an operational amplifier and a diode, the positive input terminal of the operational amplifier being connected to the first terminal, the negative input terminal of the operational amplifier receiving the reference voltage, the output terminal of the operational amplifier being connected to the anode of the diode, and the cathode of the diode being connected to the second terminal.

[0018] (10) In the conversion circuit of (9) above, the positive power supply terminal of the operational amplifier may be connected to the third terminal, and the negative power supply terminal of the operational amplifier may be connected to the second terminal.

[0019] (11) In at least one of the conversion circuits described above in (1) to (10), the output impedance of the conversion circuit may be 1 Ω or less.

[0020] (12) Furthermore, at least one of the conversion circuits of (1) to (11) above may include at least one of a power supply resistor having one end connected to the third terminal and the other end connected to a power supply voltage, a capacitor having one end connected to the third terminal and the other end serving as an output end to the load side, and a capacitor having one end connected to the third terminal and the other end connected to the first terminal.

[0021] (13) In order to achieve the above object, an electronic circuit according to one embodiment of the present invention is an electronic circuit comprising at least one conversion circuit selected from the above (1) to (12) and comprising a sensor connected to the input section.

[0022] (14) In the electronic circuit of (13) above, the sensor may be one of a condenser microphone, a piezoelectric sensor, a pressure sensor, an acceleration sensor, an optical sensor, and a quartz crystal oscillator. Effect of the Invention

[0023] According to (1) to (14), it is possible to reduce the superimposition of noise. [Brief description of the drawings]

[0024] [Figure 1] 2 is a diagram showing a condenser microphone, a power supply circuit, and an equivalent circuit at the operating point of the condenser microphone unit. FIG. [Diagram 2] FIG. 2 is a diagram illustrating an example of an electronic circuit according to the first embodiment. [Diagram 3]FIG. 11 is a diagram illustrating an example of an electronic circuit according to a second embodiment. [Figure 4] FIG. 13 is a diagram showing a modified example of the second embodiment. [Diagram 5] 10A and 10B are diagrams illustrating an example of a signal waveform when an audio signal is collected using a microphone unit. [Figure 6] FIG. 13 is a diagram showing an example of a result of actually measuring a power supply rejection ratio. [Figure 7] This is an example of the results of measuring the relationship between the power supply voltage Vcc in an electronic circuit and the output voltage output from the output terminal Vout. [Figure 8] FIG. 13 is a diagram illustrating a configuration example of an electronic circuit according to a third embodiment. [Figure 9] FIG. 11 is a diagram showing the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout in the third embodiment. [Figure 10] FIG. 13 is a diagram illustrating an example of the configuration of an electronic circuit according to a fourth embodiment. [Figure 11] FIG. 13 is a diagram showing the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout in the fourth embodiment. [Figure 12] FIG. 13 is a diagram illustrating an example of the configuration of an electronic circuit according to a fifth embodiment. [Figure 13] FIG. 13 is a diagram showing the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout in the fifth embodiment. [Figure 14] FIG. 13 is a diagram showing an example of the configuration of an electronic circuit when the sensor is a quartz crystal oscillator. [Figure 15] FIG. 1 is a diagram showing a conventional microphone circuit and example input and output signals. [Figure 16] FIG. 13 is a diagram illustrating an example of the configuration of an electronic circuit according to a sixth embodiment. [Figure 17] FIG. 13 is a diagram illustrating a configuration example of an electronic circuit according to a seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings used in the following description, the scale of each component is appropriately changed so that each component is of a recognizable size. In addition, in all the drawings for explaining the embodiments, the same reference numerals are used for the parts having the same functions, and the repeated explanation is omitted. In addition, "based on XX" in this application means "based on at least XX," and includes cases where it is based on other elements in addition to XX. Furthermore, "based on XX" is not limited to cases where XX is used directly, but also includes cases where it is based on XX that has been calculated or processed. "XX" is any element (for example, any information).

[0026] First, a general circuit when using a condenser microphone and an equivalent circuit at the operating point of the condenser microphone unit will be described. FIG. 1 is a diagram showing a condenser microphone, a power supply circuit, and an equivalent circuit at an operating point of the condenser microphone unit. The diagram of reference g11 is an example of a condenser microphone and a power supply circuit. As shown in the diagram of reference g11, the condenser microphone unit ECM is, for example, a condenser microphone C m and resistor R m And, FETQ m Equipped with a condenser microphone C m One end is resistor R m One end of FETQ m The other end is connected to the gate of resistor R m The other end of the FETQ is connected to ground. m The drain is connected to resistor R L One end of the capacitor C O The resistor R L The other end of the capacitor C is connected to the power supply voltage Vcc. O The other end is the output terminal V out is connected to.

[0027] Resistance R m FETQm is the input bias resistor of FETQ m Resistor R L The power supply voltage Vcc is m The load resistance is the capacitor C O is a capacitor for cutting AC components.

[0028] The diagram of reference symbol g12 is an equivalent circuit at the operating point of the condenser microphone unit ECM. m and resistor R m and the current source g m and fixed resistor R mO It can be expressed as:

[0029] As explained using Figure 1, the equivalent circuit of the condenser microphone unit ECM can be considered as a current source. Therefore, in order to reduce the power supply noise ΔVcc that appears on the power supply voltage Vcc, it is sufficient to use a circuit configuration that does not include the power supply noise ΔVcc in the output term.

[0030] (First embodiment) Fig. 2 is a diagram showing an example of an electronic circuit according to the first embodiment. As shown in Fig. 2, an electronic circuit 1 includes a sensor 2 and a conversion circuit 3. Note that in the following embodiments, a microphone unit is used as an example of the sensor 2, but the sensor 2 is not limited to a microphone unit and may be, for example, a piezoelectric sensor as described later.

[0031] The sensor 2 is, for example, a condenser microphone unit ECM. The sensor 2 is, for example, a condenser microphone C m and resistor R a and a field effect transistor Tr1. The conversion circuit 3 includes, for example, a capacitor C f and resistor R b (first resistor) and the reference power supply V refThe conversion circuit 3 includes a resistor R L (power supply resistor) and capacitor C O The device may include: The regulator 101 includes, for example, an operational amplifier 31, a transistor Tr2 (first transistor), and a reference power supply V ref The conversion circuit 3 also includes a capacitor C f The above configuration may not be provided.

[0032] Next, the connection configuration of the conversion circuit 3 will be described. Capacitor C f One end is resistor R b One end of resistor R L One end of the capacitor C O One end of the resistor R b The other end of the resistor is connected to the positive input terminal (+) of the operational amplifier 31 and the output of the sensor 2 .

[0033] The negative input terminal (-) of the operational amplifier 31 is connected to the reference power supply V ref The positive power supply terminal +V of the operational amplifier 31 is connected to the positive electrode of the resistor R L The negative power supply terminal -V is connected to one end of the first power supply terminal of the first transistor, the negative power supply terminal -V is connected to ground, and the emitter of the transistor Tr2 is connected to ground.

[0034] Reference power supply V ref The negative terminal of is connected to ground. ref may be, for example, a Zener diode circuit. In this case, for example, one end of another first resistor (not shown) is connected to a resistor R L the other end of the other first resistor is connected to the cathode of another first Zener diode (not shown) and the negative input terminal of the operational amplifier 31, and the anode of the other first Zener diode is connected to ground.

[0035] Resistance R LThe other end is connected to a power supply voltage Vcc. Capacitor C O The other end is connected to the output terminal Vout.

[0036] Next, in the conversion circuit 3, a first terminal, a second terminal, and a third terminal are defined. In the conversion circuit 3, the output terminal of the sensor 2 (the drain of the field effect transistor Tr1) and the resistor R b and the other end of the capacitor C f The intersection of the other end of this terminal and the positive input terminal of the operational amplifier 31 is defined as a first terminal pin1. In this manner, the first terminal pin1 is the input section of the conversion circuit 3. In addition, the voltage of the first terminal pin1 is defined as Vpin1. Transistor Tr2 emitter and reference power supply V ref The intersection of the negative poles of these is defined as the second terminal pin2. The second terminal pin2 is ground. The negative power supply terminal -V of the operational amplifier 31 is connected to the second terminal pin2. Resistance R b One end of the capacitor C f One end of the transistor Tr2 and the collector of the resistor R L One end of the capacitor C O The intersection of these two terminals is the third terminal pin3. In this manner, the third terminal pin3 is both a power supply and an output of the conversion circuit 3. The positive power supply terminal +V of the operational amplifier 31 is connected to the third terminal pin3. The positive power supply terminal +V and the negative power supply terminal -V of the operational amplifier 31 may be connected to another external power supply (not shown) instead of being connected to the third terminal pin3 and the second terminal pin2.

[0037] In the conversion circuit 3, the resistor R b The gain (R bThe current Is is the signal current of the condenser microphone unit ECM. In the conversion circuit 3, an operational amplifier 31 is, for example, an op-amp, and serves as an error circuit that detects the error between the signal input to the positive input terminal and the voltage of a reference power supply. The signal current of the condenser microphone unit ECM is converted to a voltage by the conversion circuit 3. The regulator 101 controls the output voltage. The regulator 101 controls the output voltage by a sink current. That is, regulator 101 detects the difference between the voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts the amount of current flowing from the third terminal to the second terminal according to the magnitude of the difference to a value possible within the specification range of the power supply voltage and current, lowers the voltage of the third terminal, and controls so as to maintain the voltage of the first terminal at the reference voltage. Also, the current flowing from the third terminal to the second terminal is a sink current (current sink). On the other hand, if the voltage at the first terminal is lower than the reference voltage, it adjusts the sink current and increases the voltage at the third terminal to the maximum possible value within the specified range of the power supply voltage and current, thereby maintaining the voltage at the first terminal at the reference voltage. Furthermore, when the voltage at the first terminal is equal to the reference voltage, the amount of sink current is maintained, and the voltage at the first terminal and the reference voltage are also maintained equal. In this way, the voltage Vpin1 of the first terminal is controlled by the reference power supply V ref The voltage for the sensor is applied to the condenser microphone unit ECM.

[0038] By the way, the signal current of the condenser microphone unit ECM, which is the sensor, is I s The first terminal pin1 outputs I s But resistance R b The voltage of the first terminal, Vpin1, is approximately equal to the reference power supply V ref When the output voltage is approximately equal to V ref +I s ×R b The voltage is expressed as: As described above, according to the configuration of this embodiment, the feedback circuit works sufficiently to reduce the output impedance at the third terminal, making it robust against external noise. Furthermore, since the output part of the conversion circuit has a current sink structure rather than a current source structure, in this embodiment, the power supply part and the output part of the conversion circuit can be made into the same terminal, which contributes to operation with only a weak voltage application for the sensor. These are also common to the conversion circuits (3A, 3B, 3C, 3D, 3E, and 3F) described later.

[0039] Since the output of the conversion circuit 3 does not include the power supply noise ΔVcc in the output term, the conversion circuit 3 of this embodiment has a circuit configuration that is robust against external noise. As a result, this embodiment can reduce power supply noise superimposed on the microphone output. Since this embodiment can reduce noise, it is possible to record and play back even low-level signals without being buried in noise, as compared to the conventional technique.

[0040] (Second Example) Fig. 3 is a diagram showing an example of an electronic circuit according to Example 2. As shown in Fig. 3, an electronic circuit 1A includes a sensor 2 and a conversion circuit 3A. The sensor 2 is, for example, a condenser microphone unit ECM. The sensor 2 is, for example, a condenser microphone C m and resistor R a and a field effect transistor Tr1. The conversion circuit 3A includes, for example, a capacitor C f and resistor R b (first resistor) and a variable shunt regulator 32. The conversion circuit 3A includes a resistor R L (power supply resistor) and capacitor C O The device may include: In the conversion circuit 3A, the regulator 101A is a variable shunt regulator 32. The conversion circuit 3A also includes a capacitor C f The above configuration may not be provided.

[0041] Next, the connection configuration of the conversion circuit 3A will be described. Capacitor C f One end is resistor R b One end of resistor R L One end of the capacitor C O and the cathode of the variable shunt regulator 32, and the other end is connected to the resistor R b The other end of the resistor R1 is connected to a reference terminal of the variable shunt regulator 32 and the output of the sensor 2 (the drain of the field effect transistor Tr1). The anode of the variable shunt regulator 32 is connected to ground. Resistance R L The other end is connected to a power supply voltage Vcc. Capacitor C O The other end is connected to the output terminal Vout.

[0042] Next, in the conversion circuit 3A, a first terminal, a second terminal, and a third terminal are defined. In the conversion circuit 3A, the output terminal of the sensor 2 (the drain of the field effect transistor Tr1) and the resistor R b The other end of the capacitor C f The intersection of the other end of this terminal and the reference terminal of the variable shunt regulator 32 is defined as the first terminal pin1. In this manner, the first terminal pin1 is the input section of the conversion circuit 3A. The voltage of the first terminal pin1 is defined as Vpin1. The anode of the variable shunt regulator 32 is the second terminal pin2. The second terminal pin2 is ground. Resistance R b One end of the capacitor C f One end of the resistor R L One end of the capacitor C O The intersection of these two terminals is defined as the third terminal pin3. In this manner, the third terminal pin3 is both a power supply part and an output part of the conversion circuit 3A.

[0043] In addition, in the conversion circuit 3A, the resistor R b The gain (R bIn addition, regulator 101A (variable shunt regulator 32) controls the output voltage. The output voltage of regulator 101A is controlled by a sink current. In this configuration, the reference voltage V ref is the voltage between the reference terminal and the second terminal pin2 of the variable shunt regulator 32. Regulator 101A (variable shunt regulator 32) detects the difference between the voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts the amount of current flowing from the third terminal to the second terminal according to the magnitude of the difference to a value possible within the specification range of the power supply voltage and current, lowers the voltage of the third terminal, and controls so as to maintain the voltage of the first terminal at the reference voltage. The current flowing from the third terminal to the second terminal is a sink current (current sink). When the voltage of the first terminal is in the same state as when it is lower than the reference voltage, it operates in the same way as in the first embodiment.

[0044] In the configuration of FIG. 3, the equivalent circuit of the variable shunt regulator 32 is the same as that of the operational amplifier 31 and the reference power supply V ref That is, according to this embodiment, the conversion circuit 3 of the first embodiment is realized by using the variable shunt regulator 32, so that the reference power supply V ref 2. In other words, in the configuration of the second embodiment, the equivalent circuit of variable shunt regulator 32 can be expressed by the equivalent circuit of the configuration in FIG. As a result, this embodiment can reduce power supply noise superimposed on the microphone output. Since this embodiment can reduce noise, it is possible to record and play back even low-level signals without being buried in noise, as compared to the conventional technique.

[0045] FIG. 4 is a diagram showing a modification of the second embodiment. Figure 4 shows the resistor R L and capacitor C OThe device is a device to which the outputs of the sensor 2 and the conversion circuit 3A are input, such as a recording device or an IC recorder. Such a configuration in which the device supplies power to the microphone is called, for example, a "plug-in power system." The conversion circuit 3A operates even when a voltage is applied to the sensor (microphone) that is vulnerable to external noise, and unlike the conventional technology, can be placed near the sensor where it is sometimes difficult to prepare a stable power source. Note that the above-mentioned conversion circuit 3 and the conversion circuits 3B, 3C, and 3D described later may also be configured to supply power to the microphone on the device side as shown in FIG. 4.

[0046] If the device is, for example, an IC recorder, the device also contains digital circuits, which may cause digital noise to be present on the power supply. As explained in the prior art with reference to Figure 15, if the sensor 2 is directly connected to the device, the impact of such power supply noise is significant.

[0047] In the circuit configurations of Figs. 3 and 4, the output impedance can be made much lower than that of the condenser microphone unit ECM. For example, the measured output impedance for the DC component was 2.6 kΩ for the condenser microphone unit ECM and 0.42 Ω for the conversion circuit 3A. The measured output impedance for the 1 kHz AC component was 1.9 kΩ for the condenser microphone unit ECM and 0.37 Ω for the conversion circuit 3A. In this way, the circuit configuration of this embodiment can reduce the output impedance, making it robust against external noise including power supply noise and transmission line noise. Note that the above measured values ​​are merely examples and are not limiting.

[0048] 5 is a diagram showing an example of a signal waveform when an audio signal is collected using a microphone unit. For the confirmation, the audio signal when "Ah~~" is pronounced into the condenser microphone is collected. The waveform of reference g21 is a waveform obtained by connecting a resistor R L and capacitor C Oand resistor R L The power supply (Vcc) is supplied via noise of 100mV. p-p The waveform of the signal g22 is obtained by connecting the converter circuit 3A to the condenser microphone unit ECM and L and capacitor C O and resistor R L The noise on the power supply is 100mV. p-p The output signal waveform when the two signals are superimposed is shown in Fig. 5. In Fig. 5, the horizontal axis is time (seconds) and the vertical axis is output voltage (V). The measurement conditions are Vcc of 2.7 V and R L is 2.2kΩ. As shown in FIG. 5, as a result of using the conversion circuit 3A of this embodiment, even when power supply noise is superimposed, the effect on the output signal can be reduced.

[0049] Next, an example of the actual measurement result of the power supply voltage fluctuation rejection ratio, which is a quantitative evaluation of the power supply noise rejection effect shown qualitatively in FIG. 5, will be described. FIG. 6 is a diagram showing an example of the results of actually measuring the power supply rejection ratio. The horizontal axis is frequency (Hz), and the vertical axis is the power supply rejection ratio PSRR (Power Supply Rejection Ratio) (dB). Line g31 is the PSRR of the condenser microphone unit ECM without the conversion circuit 3A. When the conversion circuit 3A is not provided, the PSRR is about 1.3 dB, and as described with reference to FIG. 1, it can be seen that the power supply noise ΔVcc on the power supply voltage Vcc is not attenuated and is superimposed on ΔVout as it is. In contrast, line g32 is the PSRR when the conversion circuit 3A is used. When the conversion circuit 3A is provided, the PSRR is 67 dB, and it can be seen that the power supply noise ΔVcc can be significantly removed compared to when the conversion circuit 3A is not provided. Note that the measured values ​​shown in FIG. 6 are merely an example, and are not limited to this. In this way, by using the conversion circuit 3A of this embodiment, the PSRR can be improved by 65 dB or more, that is, the amplitude of the power supply noise can be reduced to about 1 / 1000.

[0050] Next, the relationship between the power supply voltage Vcc in the electronic circuit and the output voltage output from the output terminal Vout will be described. FIG. 7 shows an example of the results of an actual measurement of the relationship between the power supply voltage Vcc in an electronic circuit and the output voltage output from the output terminal Vout. The horizontal axis is the power supply voltage Vcc (V), and the vertical axis is the output voltage (V) output from the output terminal Vout. Line g41 is the measurement result of a condenser microphone unit ECM that does not include the conversion circuit 3A, and line g42 is the measurement result when the conversion circuit 3A is included. The measurement conditions were R b 2.2kΩ, C f The specified characteristics of the condenser microphone used in the measurement are a sensitivity of -42.0±2.0 dB at 1 kHz, a recommended power supply voltage of 1.5 V, and a resistance R L The recommended value of is 1.0 kΩ, the power supply voltage range is 1.0 to 10.0 V, and the frequency characteristics are 50 to 16000 Hz. The specified characteristics of the variable shunt regulator used in the conversion circuit 3A are that the voltage value to the reference terminal is 1.24 V, the output impedance is typically 0.25 Ω, and the output voltage is from the voltage value to the reference terminal to 18 V. That is, in this embodiment, the output impedance of the conversion circuit 3A is set to 1 Ω or less.

[0051] As shown in FIG. 7, when the conversion circuit 3A is not used, the output voltage output from the output terminal Vout fluctuates depending on the power supply voltage Vcc, as shown in the graph having a slope in each section, and the fluctuations in the power supply voltage Vcc become noise. On the other hand, according to the configuration of this embodiment, when the converter circuit 3A is provided, the output voltage output from the output terminal Vout is constant regardless of the power supply voltage Vcc under the condition that the power supply voltage Vcc is 2.1V or more, so that even if the power supply voltage Vcc fluctuates, noise does not occur. Also, according to the configuration of this embodiment, the output impedance can be reduced, so that the configuration is robust against external noise. And, according to this embodiment, since the noise can be reduced, even a low-level signal can be recorded and played back without being buried in noise, compared to the conventional case.

[0052] (Third Example) Next, an example in which Darlington-connected transistors are used in a conversion circuit will be described. Fig. 8 is a diagram showing an example of the configuration of an electronic circuit according to Example 3. As shown in Fig. 8, an electronic circuit 1B includes a sensor 2 and a conversion circuit 3B. The sensor 2 is, for example, a condenser microphone unit ECM. The condenser microphone unit ECM is, for example, a condenser microphone C m and resistor R a and a field effect transistor Tr1. The conversion circuit 3B includes, for example, a capacitor C f and resistor R b (first resistor), transistor Tr3 (first transistor), transistor Tr4 (second transistor), and resistor R c (second resistor). The conversion circuit 3B includes a resistor R L (power supply resistor) and capacitor C O The conversion circuit 3B may also include a capacitor C f The transistors Tr3 and Tr4 are NPN type transistors. The regulator 101B includes, for example, a transistor Tr3 (first transistor), a transistor Tr4 (second transistor), and a resistor R c (Third resistor).

[0053] Next, the connection configuration of the conversion circuit 3B will be described. Capacitor C f One end is resistor R b One end of resistor R L One end of the capacitor C O One end of the resistor R is connected to the collector of the transistor Tr3 and the collector of the transistor Tr4. b The other end of the resistor is connected to the base of the transistor Tr3 and the output of the sensor 2.

[0054] The emitter of the transistor Tr3 is connected to the resistor R cand the base of the transistor Tr4. The transistors Tr3 and Tr4 are connected in a Darlington configuration.

[0055] Resistance R c The other end is connected to ground. The emitter of the transistor Tr4 is connected to ground. Resistance R L The other end is connected to a power supply voltage Vcc. Capacitor C O The other end is connected to the output terminal Vout.

[0056] Next, in the conversion circuit 3B, a first terminal, a second terminal, and a third terminal are defined. In the conversion circuit 3B, the output terminal of the sensor 2 (the drain of the field effect transistor Tr1) and the resistor R b and the other end of the capacitor C f The intersection of the other end of the first terminal pin1 and the base of the transistor Tr3 is defined as the first terminal pin1. In this manner, the first terminal pin1 is the input section of the conversion circuit 3B. The voltage of the first terminal pin1 is defined as Vpin1. Transistor Tr4 emitter and resistor R c The intersection with the other end of the first terminal is defined as the second terminal pin2. The second terminal pin2 is ground. Resistance R b One end of the capacitor C f One end of the transistor Tr3, the collector of the transistor Tr4, and the resistor R L One end of the capacitor C O The intersection of these two terminals is defined as the third terminal pin3. In this manner, the third terminal pin3 is both a power supply part and an output part of the conversion circuit 3B.

[0057] In the conversion circuit 3B, the resistor R b The gain (R b The output voltage of regulator 101B is controlled by a sink current. In this configuration, the reference voltage Vref is the voltage between the base of the transistor Tr3 and the second terminal pin2. In this embodiment, regulator 101B detects the difference between the voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts the amount of current flowing from the third terminal to the second terminal according to the magnitude of the difference to a value possible within the specification range of the power supply voltage and current, lowers the voltage of the third terminal, and controls so as to maintain the voltage of the first terminal at the reference voltage. Also, the current flowing from the third terminal to the second terminal is a sink current (current sink). Note that when the voltage of the first terminal is in the same state as when it is lower than the reference voltage, it operates in the same way as in the first embodiment.

[0058] 9 is a diagram showing the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout in the third embodiment. The horizontal axis is the power supply voltage Vcc (V), and the vertical axis is the output voltage Vout (V) output from the output terminal Vout. The measurement conditions in FIG. 9 are as follows: the sensor 2 is connected to a current source g m and resistor R mo When the equivalent circuit is considered as shown in Figure 1, the resistance R mo is 100 kΩ, and resistor R b is 2.2 kΩ, and resistor R L is 2.2kΩ. Also, the resistance R c are 10 kΩ (wire g51), 100 kΩ (wire g52), 1 MΩ (wire g53), and 10 MΩ (wire g54). This means that the resistance R c This shows that the reference voltage can be adjusted by the value of . The current output value of the current source gm is 0.16 mA.

[0059] In the configuration of the third embodiment, the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout is as shown in Fig. 9, so when the power supply voltage Vcc is about 2V or more, even if the power supply voltage Vcc changes, the output voltage output from the output terminal Vout remains almost constant, so the influence of noise on the power supply voltage Vcc can be reduced. Furthermore, according to this embodiment, since noise can be reduced, even signals with lower levels than before can be recorded and played back without being buried in noise.

[0060] (Fourth Example) A second example in which Darlington-connected transistors are used in the conversion circuit will be described. Fig. 10 is a diagram showing an example of the configuration of an electronic circuit according to Example 4. As shown in Fig. 10, an electronic circuit 1C includes a sensor 2 and a conversion circuit 3C. The sensor 2 is, for example, a condenser microphone unit ECM. The condenser microphone unit ECM is, for example, a condenser microphone C m and resistor R a and a field effect transistor Tr1. The conversion circuit 3C includes, for example, a capacitor C f and resistor R b (first resistor), a transistor Tr5 (first transistor), a transistor Tr6 (second transistor), a transistor Tr7 (third transistor), a transistor Tr8 (fourth transistor), and a resistor R d (second resistor) and resistor R e (third resistor) and resistor R f (fourth resistor). The conversion circuit 3C includes a resistor R L (power supply resistor) and capacitor C O The conversion circuit 3C may also include a capacitor C f The transistors Tr5, Tr6, and Tr8 are NPN type transistors, and the transistor Tr7 is a PNP type transistor. The regulator 101C includes, for example, a transistor Tr5 (first transistor), a transistor Tr6 (second transistor), a transistor Tr7 (third transistor), a transistor Tr8 (fourth transistor), and a resistor R d (second resistor) and resistor R e (third resistor) and resistor R f (4th resistor).

[0061] Next, the connection configuration of the conversion circuit 3C will be described. Capacitor C f One end is resistor R b One end of resistor RL One end of the capacitor C O One end of the transistor Tr5 and the collector of the resistor R e One end of the resistor R is connected to the emitter of transistor Tr7 and the collector of transistor Tr8. b The other end of this resistor is connected to the base of the transistor Tr5 and the output of the sensor 2.

[0062] The emitter of transistor Tr5 is connected to resistor R d and the base of transistor Tr6. Transistors Tr5 and Tr6 are connected in a Darlington configuration. Resistance R d The other end is connected to ground.

[0063] The collector of the transistor Tr6 is connected to resistor R e The other end of the transistor Tr7 is connected to the base of the transistor Tr7, and the emitter of the transistor Tr7 is connected to ground. The collector of the transistor Tr7 is connected to the resistor R f and the base of the transistor Tr8. The transistors Tr7 and Tr8 are connected in an inverted Darlington configuration.

[0064] Resistance R f The other end is connected to ground. The emitter of transistor Tr8 is connected to ground. Resistance R L The other end is connected to a power supply voltage Vcc. Capacitor C O The other end is connected to the output terminal Vout.

[0065] Next, in the conversion circuit 3C, a first terminal, a second terminal, and a third terminal are defined. In the conversion circuit 3C, the output terminal of the sensor 2 (the drain of the field effect transistor Tr1) and the resistor R b The other end of the capacitor C fThe intersection of the other end of the first terminal pin1 and the base of the transistor Tr5 is defined as the first terminal pin1. In this manner, the first terminal pin1 is the input section of the conversion circuit 3C. The voltage of the first terminal pin1 is defined as Vpin1. Transistor Tr8 emitter and resistor R f The other end of the resistor R d The intersection with the other end of the first terminal is defined as the second terminal pin2. The second terminal pin2 is ground. Resistance R b One end of the capacitor C f One end of the transistor Tr5 and the collector of the resistor R e One end of the transistor Tr7, the emitter of the transistor Tr8, and the resistor R L One end of the capacitor C O The intersection of these two terminals is defined as the third terminal pin3. In this manner, the third terminal pin3 is both a power supply part and an output part of the conversion circuit 3C.

[0066] In addition, in the conversion circuit 3C, the resistor R b The gain (R b The regulator 101C controls the output voltage by a sink current. In this configuration, the reference voltage V ref is the voltage between the base of the transistor Tr5 and the second terminal pin2. Regulator 101C detects the difference between the voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts the amount of current flowing from the third terminal to the second terminal according to the magnitude of the difference to a value possible within the specification range of the power supply voltage and current, lowers the voltage of the third terminal, and controls so as to maintain the voltage of the first terminal at the reference voltage. Also, the current flowing from the third terminal to the second terminal is a sink current (current sink). When the voltage at the first terminal is in the same state as when it is lower than the reference voltage, the operation is the same as in the first embodiment.

[0067] 11 is a diagram showing the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout in the fourth embodiment. The horizontal axis is the power supply voltage Vcc (V), and the vertical axis is the output voltage (V) output from the output terminal Vout. The measurement conditions in FIG. 11 are as follows: the sensor 2 is connected to a current source g m and resistor R mo When the equivalent circuit is considered as shown in Figure 1, the resistance R mo is 100 kΩ, and resistor R b is 2.2 kΩ, and resistor R e is 10 kΩ, and resistor R f is 5 kΩ, and resistor R L is 2.2kΩ. Also, the resistance R d are 10 kΩ (line g61), 100 kΩ (line g62), 1 MΩ (line g63), and 10 MΩ (line g64). d This shows that the reference voltage can be adjusted by the value of . The current output value of the current source gm is 0.16 mA.

[0068] In the configuration of the fourth embodiment, the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout is as shown in Figure 11, so when the power supply voltage Vcc is about 2V or more, even if the power supply voltage Vcc changes, the output voltage output from the output terminal Vout is constant, so the influence of noise on the power supply voltage Vcc can be reduced. And, according to this embodiment, since noise can be reduced, even small level signals can be recorded and played back without being buried in noise compared to the conventional art. In particular, the flat part in Figure 11 has a much smaller slope than Figure 9 of the third embodiment, and it can be seen that the output impedance and resistance to external noise of the fourth embodiment are particularly superior to the third embodiment.

[0069] (Fifth Example) A third example in which Darlington-connected transistors are used in a conversion circuit will be described. Fig. 12 is a diagram showing an example of the configuration of an electronic circuit according to Example 5. As shown in Fig. 12, an electronic circuit 1D includes a sensor 2 and a conversion circuit 3D. The sensor 2 is, for example, a condenser microphone unit ECM. The condenser microphone unit ECM is, for example, a condenser microphone Cm and resistor R a and a field effect transistor Tr1. The conversion circuit 3D is, for example, a capacitor C f and resistor R b (first resistor), a transistor Tr9 (first transistor), a transistor Tr10 (second transistor), a transistor Tr11 (third transistor), and a resistor R g (second resistor) and resistor R h (third resistor). The conversion circuit 3D is equipped with a resistor R L (power supply resistor) and capacitor C O The conversion circuit 3D may also include a capacitor C f The transistors Tr9 and Tr10 are NPN type transistors, and the transistor Tr11 is a PNP type transistor. The regulator 101D includes, for example, a transistor Tr9 (first transistor), a transistor Tr10 (second transistor), a transistor Tr11 (third transistor), and a resistor R g (second resistor) and resistor R h (Third resistor).

[0070] Next, the connection configuration of the conversion circuit 3D will be described. Capacitor C f One end is resistor R b One end of resistor R L One end of the capacitor C O One end of the transistor Tr9 and the collector of the resistor R h One end of the resistor R b The other end of this resistor is connected to the base of the transistor Tr9 and the output of the sensor 2 (the drain of the field effect transistor Tr1).

[0071] The emitter of the transistor Tr9 is connected to the resistor R g and the base of transistor Tr10. Transistors Tr9 and Tr10 are connected in a Darlington configuration. Resistance Rg The other end is connected to ground.

[0072] The collector of the transistor Tr10 is connected to resistor R h The other end of this terminal is connected to the base of a transistor Tr11, and the emitter of this terminal is connected to ground. The collector of the transistor Tr11 is connected to the ground. Resistance R L The other end is connected to a power supply voltage Vcc. Capacitor C O The other end is connected to the output terminal Vout.

[0073] Next, in the conversion circuit 3D, a first terminal, a second terminal, and a third terminal are defined. In the conversion circuit 3D, the output terminal of sensor 2 (the drain of the field effect transistor Tr1) and resistor R b The other end of the capacitor C f The intersection of the other end of the first terminal pin1 and the base of the transistor Tr9 is defined as the first terminal pin1. In this manner, the first terminal pin1 is the input section of the conversion circuit 3D. The voltage of the first terminal pin1 is defined as Vpin1. The collector of transistor Tr11, the emitter of transistor Tr10, and resistor R g The intersection point with the other end of the resistor R is the second terminal pin2. The second terminal pin2 is ground. b One end of the capacitor C f One end of the transistor Tr9 and the collector of the resistor R h One end of the transistor Tr11 and the emitter of the resistor R L One end of the capacitor C O The intersection at one end of these terminals is the third terminal pin3. In this manner, the third terminal pin3 is both a power supply portion and an output portion of the conversion circuit 3D.

[0074] In addition, in the conversion circuit 3D, the resistor R b The gain (R b The regulator 101D controls the output voltage by a sink current. In this configuration, the reference voltage V ref is the voltage between the base of the transistor Tr9 and the second terminal pin2. Regulator 101D detects the difference between the voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts the amount of current flowing from the third terminal to the second terminal according to the magnitude of the difference as much as the power supply voltage and current allow, lowers the voltage of the third terminal, and controls so as to maintain the voltage of the first terminal at the reference voltage. Also, the current flowing from the third terminal to the second terminal is a sink current (current sink). When the voltage at the first terminal is in the same state as when it is lower than the reference voltage, the operation is the same as in the first embodiment.

[0075] 13 is a diagram showing the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout in the fifth embodiment. The horizontal axis is the power supply voltage Vcc (V), and the vertical axis is the output voltage Vout (V) output from the output terminal Vout. The measurement conditions in FIG. 13 are as follows: the sensor 2 is connected to a current source g m and resistor R mo When the equivalent circuit is considered as shown in Figure 1, the resistance R mo is 100 kΩ, and resistor R b is 2.2 kΩ, and resistor R h is 10 kΩ, and resistor R L is 2.2kΩ. Also, the resistance R g are 10 kΩ (wire g71), 100 kΩ (wire g72), 1 MΩ (wire g73), and 10 MΩ (wire g74). g The reference voltage can be adjusted by the value of . The current output value of the current source gm is 0.16 mA.

[0076] In the configuration of the fifth embodiment, the relationship between the power supply voltage Vcc and the output voltage output from the output terminal Vout is as shown in Fig. 13, so when the power supply voltage Vcc is about 2V or more, even if the power supply voltage Vcc changes, the output voltage output from the output terminal Vout remains constant, so the influence of noise on the power supply voltage Vcc can be reduced. Furthermore, according to this embodiment, since noise can be reduced, even signals with lower levels than before can be recorded and played back without being buried in noise, making it possible to balance mountability and resistance to external noise.

[0077] (Example of a sensor) In the above-described embodiments, the sensor 2 is a condenser microphone unit, but the present invention is not limited to this. The sensor 2 may be, for example, a condenser microphone alone, or may be a sensor with high output impedance, such as a pressure sensor, a piezoelectric sensor, a quartz crystal unit, an acceleration sensor, or an optical sensor.

[0078] FIG. 14 is a diagram showing an example of the configuration of an electronic circuit when the sensor is a quartz crystal oscillator. A quartz crystal unit generally has a high impedance, for example, several tens of kΩ, and therefore may introduce noise when connected to another circuit. For this reason, a configuration is known in which the impedance is reduced by combining a quartz crystal unit X with a field effect transistor Tr21, as in the sensor 2E in FIG. 14. In the configuration of the sensor 2E in FIG. 14, the impedance is reduced to, for example, 10 14 The impedance can be reduced from 0.1Ω to about 100Ω. In an electronic circuit 1E in which the above-mentioned conversion circuit 3A is connected to such a sensor 2E, the output impedance can be further reduced, so that the influence of noise can be further reduced. The conversion circuit may be the above-mentioned conversion circuits 3, 3B, 3C, and 3D.

[0079] Furthermore, since quartz has a piezoelectric effect, for example, in a piezoelectric acceleration sensor, a configuration is known in which a capacitor and a resistor are connected in parallel to the quartz crystal X between the quartz crystal X and the field effect transistor Tr21 (see, for example, Reference 1). By connecting the above-mentioned conversion circuit 3 or the like to such a sensor, the output impedance can be further reduced, and the influence of noise can be further reduced. And, according to this embodiment, since noise can be reduced, even a signal with a lower level can be detected without being buried in noise, compared to the conventional case.

[0080] Reference 1; Accelerometer conversion types (piezoelectric (PE), piezoresistive (PR), and capacitive (VC) sensors), Toyo Corporation, 2022.02.16, Internet search, 2022.10.26,<URL;https: / / www.toyo.co.jp / mecha / casestudy / detail / id=34295>

[0081] (Sixth Example) Next, an example in which a field effect transistor (FET) is used in the conversion circuit will be described. Fig. 16 is a diagram showing an example of the configuration of an electronic circuit according to Example 6. As shown in Fig. 16, an electronic circuit 1F includes a sensor 2 and a conversion circuit 3E. The sensor 2 is, for example, a condenser microphone unit ECM. The condenser microphone unit ECM is, for example, a condenser microphone C m and resistor R a and a field effect transistor Tr1. The conversion circuit 3E includes, for example, a capacitor C f and resistor R b (first resistor), a field effect transistor FET1 (first field effect transistor), a field effect transistor FET2 (second field effect transistor), and a resistor R i (second resistor). The conversion circuit 3E includes a resistor R L (power supply resistor) and capacitor C O The conversion circuit 3E may also include a capacitor C fIn addition, the field effect transistor FET1 and the field effect transistor FET2 may be any type of FET, such as a MOSFET, a MESFET, a SiC FET, a GaN FET, or a GaAs FET. The regulator 101E includes, for example, a field effect transistor FET1 (first field effect transistor), a field effect transistor FET2 (second field effect transistor), and a resistor R i (Second resistor).

[0082] Next, the connection configuration of the conversion circuit 3E will be described. Capacitor C f One end is resistor R b One end of resistor R L One end of the capacitor C O One end of the resistor R is connected to the drain terminal t2 of the field effect transistor FET1 and the drain terminal t5 of the field effect transistor FET2. b The other end of the input is connected to a gate terminal t1 of the field effect transistor FET1 and the output of the sensor 2.

[0083] The field effect transistor FET1 has a source terminal t3 connected to a resistor R i and one end of the gate terminal t4 of the field effect transistor FET2.

[0084] Resistance R i The other end is connected to ground. The source terminal t6 of the field effect transistor FET2 is connected to ground. Resistance R L The other end is connected to a power supply voltage Vcc. Capacitor C O The other end is connected to the output terminal Vout.

[0085] Next, in the conversion circuit 3E, a first terminal, a second terminal, and a third terminal are defined. In the conversion circuit 3E, the output terminal of the sensor 2 (the drain of the field effect transistor Tr1) and the resistor R b and the other end of the capacitor C fThe intersection of the other end of the first terminal pin1 and the gate terminal t1 of the field effect transistor FET1 is defined as the first terminal pin1. In this manner, the first terminal pin1 is the input section of the conversion circuit 3E. The voltage of the first terminal pin1 is defined as Vpin1. The source terminal t6 of the field effect transistor FET2 and the resistor R i The intersection with the other end of the first terminal is defined as the second terminal pin2. The second terminal pin2 is ground. Resistance R b One end of the capacitor C f One end of the field effect transistor FET1, the drain terminal t2, the drain terminal t5 of the field effect transistor FET2, and the resistor R L One end of the capacitor C O The intersection of these two terminals is defined as the third terminal pin3. In this manner, the third terminal pin3 is both a power supply part and an output part of the conversion circuit 3E.

[0086] In the conversion circuit 3E, the resistor R b The gain (R b The output voltage of regulator 101E is controlled by a sink current. In this configuration, the reference voltage V ref is the voltage between the gate terminal t1 and the second terminal pin2 of the field effect transistor FET1. In this embodiment, regulator 101E detects the difference between the voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts the amount of current flowing from the third terminal to the second terminal to a possible value within the specification range of the power supply voltage and current according to the magnitude of the difference, lowers the voltage of the third terminal, and controls so as to maintain the voltage of the first terminal at the reference voltage. Also, the current flowing from the third terminal to the second terminal is a sink current (current sink). When the voltage at the first terminal is in the same state as when it is lower than the reference voltage, the operation is the same as in the first embodiment.

[0087] (Seventh Example) Fig. 17 is a diagram showing an example of an electronic circuit according to the seventh embodiment. As shown in Fig. 17, an electronic circuit 1G includes a sensor 2 and a conversion circuit 3F. The sensor 2 is, for example, a condenser microphone unit ECM. The condenser microphone unit ECM is, for example, a condenser microphone C m and resistor R a and a field effect transistor Tr1. The conversion circuit 3F includes, for example, a capacitor C f and resistor R b (first resistor) and the reference power supply V ref , an operational amplifier 31A, and a diode D. The conversion circuit 3F may include a resistor instead of the diode D. The conversion circuit 3F may include a resistor R L (power supply resistor) and capacitor C O The device may include: The regulator 101F includes, for example, an operational amplifier 31A, a diode D, and a reference power supply V ref Equipped with.

[0088] Next, the connection configuration of the conversion circuit 3F will be described. Capacitor C f One end is resistor R b One end of resistor R L One end of the capacitor C O is connected to one end of the resistor R b The other end of the resistor is connected to the positive input terminal (+) of the operational amplifier 31A and the output of the sensor 2.

[0089] The negative input terminal (-) of the operational amplifier 31A is connected to the reference power supply V ref The positive power supply terminal +V of the operational amplifier 31A is connected to the positive terminal of the resistor R L One end of the negative power supply terminal -V is connected to ground, and the cathode of diode D is connected to ground.

[0090] Reference power supply V ref The negative terminal of is connected to ground. refmay be, for example, a Zener diode circuit. In this case, for example, one end of another first resistor (not shown) is connected to a resistor R L the other end of the other first resistor is connected to the cathode of another first Zener diode (not shown) and the negative input terminal of the operational amplifier 31A, and the anode of the other first Zener diode is connected to ground.

[0091] Resistance R L The other end is connected to a power supply voltage Vcc. Capacitor C O The other end is connected to the output terminal Vout.

[0092] Next, in the conversion circuit 3F, a first terminal, a second terminal, and a third terminal are defined. In the conversion circuit 3F, the output terminal of the sensor 2 (the drain of the field effect transistor Tr1) and the resistor R b The other end of the capacitor C f The intersection of the other end of this terminal and the positive input terminal of the operational amplifier 31A is defined as the first terminal pin1. In this manner, the first terminal pin1 is the input section of the conversion circuit 3F. The voltage of the first terminal pin1 is defined as Vpin1. Cathode of diode D and reference power supply V ref The intersection of the negative electrodes of these terminals is defined as the second terminal pin2. The second terminal pin2 is ground. The negative power supply terminal -V of the operational amplifier 31A is connected to the second terminal pin2. Resistance R b One end of the capacitor C f One end of resistor R L One end of the capacitor C O The intersection of these two terminals is the third terminal pin3. Thus, the third terminal pin3 is a power supply section and an output section of the conversion circuit 3F. The positive power supply terminal +V of the operational amplifier 31A is connected to the third terminal pin3.

[0093] In the conversion circuit 3F, the resistor R b The gain (R bThe current Is is the signal current of the condenser microphone unit ECM. In the conversion circuit 3F, the operational amplifier 31A is, for example, an op-amp, and serves as an error circuit that detects the error between the signal input to the positive input terminal and the voltage of the reference power supply. The signal current of the condenser microphone unit ECM is converted to a voltage by the conversion circuit 3F. The regulator 101F controls the output voltage. The regulator 101F controls the output voltage by a sink current. That is, regulator 101F detects the difference between the voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts the amount of current flowing from the third terminal to the second terminal according to the magnitude of the difference to a value possible within the specification range of the power supply voltage and current, lowers the voltage of the third terminal, and controls so as to maintain the voltage of the first terminal at the reference voltage. Also, the current flowing from the third terminal to the second terminal is a sink current (current sink). On the other hand, if the voltage at the first terminal is lower than the reference voltage, it adjusts the sink current and increases the voltage at the third terminal to the maximum possible value within the specified range of the power supply voltage and current, thereby maintaining the voltage at the first terminal at the reference voltage. Furthermore, when the voltage at the first terminal is equal to the reference voltage, the amount of sink current is maintained, and the voltage at the first terminal and the reference voltage are also maintained equal. In this way, the voltage Vpin1 of the first terminal is controlled by the reference power supply V ref The voltage for the sensor is applied to the condenser microphone unit ECM.

[0094] As described above, the electronic circuit 1 (or 1A, 1B, 1C, 1D, 1F, 1G) of each embodiment is a circuit that converts the current output of the sensor 2 (or 2E) into a voltage output, and includes a conversion circuit 3 (or 3A, 3B, 3C, 3D, 3E, 3F) that outputs a voltage, and the conversion circuit 3 (or 3A, 3B, 3C, 3D, 3E, 3F) includes a first terminal pin1, a second terminal pin2, and a third terminal pin3. The electronic circuit 1 (or 1A, 1B, 1C, 1D, 1F, 1G) of each embodiment includes a power supply circuit section that supplies a constant voltage to one of the circuit, the element, and the sensor, and is connected to one of the circuit, the element, and the sensor 2 (or 2E). The second terminal pin2 of the electronic circuit 1 (or 1A, 1B, 1C, 1D, 1F, 1G) of each embodiment is grounded. Furthermore, the third terminal pin3 of the electronic circuit 1 (or 1A, 1B, 1C, 1D, 1F, 1G) in each embodiment is a power supply part and an output part of the conversion circuit 3 (or 3A, 3B, 3C, 3D, 3E, 3F). The third terminal pin3 is connected to a power supply voltage Vcc and a resistor R L The power is supplied to the conversion circuit via the

[0095] As a result, according to each of the above-mentioned embodiments, even if noise of the power supply voltage Vcc is superimposed, the influence of noise can be reduced. And, according to each of the above-mentioned embodiments, since noise can be reduced, even a signal with a lower level can be detected without being buried in noise, as compared to the conventional case. The conversion circuit (3 or 3A, 3B, 3C, 3D, 3E, 3F) can be arranged near a sensor where it may be difficult to prepare a stable power supply.

[0096] It should be noted that the conversion circuits (3 or 3A, 3B, 3C, 3D, 3E, 3F) shown in each of the above-mentioned embodiments are circuits that at first glance appear to be significantly different in appearance, but when greatly simplified, their equivalent circuits are all the same. Furthermore, the characteristics described for one conversion circuit (3 or 3A, 3B, 3C, 3D, 3E, 3F) may also apply to other conversion circuits (3 or 3A, 3B, 3C, 3D, 3E, 3F) by simply omitting repeated explanations.

[0097] The above describes the form for carrying out the present invention using examples, but the present invention is not limited to these examples in any way, and various modifications and substitutions can be made within the scope that does not deviate from the gist of the present invention.

[0098] In the sixth embodiment, the functions realized by the transistors (Tr3, Tr4) included in the conversion circuit (3B) of the third embodiment are realized by field effect transistors (FET1, FET2). Similarly, the functions realized by the transistors (Tr2, Tr5, Tr6, Tr7, Tr8, Tr9, Tr10, Tr11) included in the conversion circuits (3, 3C, 3D) of the first, fourth, and fifth embodiments can also be realized by using field effect transistors. [Explanation of symbols]

[0099] 1,1A,1B,1C,1D,1E,1F,1G...Electronic circuit, 2,2E...Sensor, 3,3A,3B,3C,3D,3E,3F...Conversion circuit, C f ,C O …capacitor, D…diode, R a ,R b ,R c ,R d ,R e ,R f ,R g ,R h ,R i ,R L ...resistor, Tr1, Tr21...field effect transistor, Tr2, Tr3, Tr,4, Tr5, Tr6, Tr7, Tr8, Tr9, Tr10, Tr11...transistor, FET1, FET2...field effect transistor, 31, 31A...operational amplifier, 32...variable shunt regulator, pin1...first terminal, pin2...second terminal, pin3...third terminal, C m …Condenser microphone, X…Crystal oscillator, V ref ...Reference power supply, Vcc...Power supply voltage, Vout...Output terminal / output voltage, 101, 101A, 101B, 101C, 101D, 101E, 101F...Regulator, Vpin1...Voltage of first terminal

Claims

1. A conversion circuit for converting an input current into an output voltage, A first terminal which is an input portion of the input current; a second terminal which is ground; a third terminal for outputting the output voltage and for supplying a power supply voltage through a power supply resistor; a first resistor having one end connected to the first terminal and the other end connected to a third terminal; a regulator that detects a difference between a voltage of the first terminal and a predetermined reference voltage, and when the voltage of the first terminal is higher than the reference voltage, adjusts an amount of current flowing from the third terminal to the second terminal in accordance with the magnitude of the difference, thereby controlling so as to maintain the voltage of the first terminal at the reference voltage; Equipped with A conversion circuit, wherein the first resistor determines a gain of the conversion circuit.

2. the current flowing from the third terminal to the second terminal is a sink current, and the sink current is supplied to the third terminal from outside the conversion circuit. The conversion circuit according to claim 1 .

3. the regulator comprises a variable shunt regulator; a reference terminal of the variable shunt regulator is connected to the first terminal; an anode terminal of the variable shunt regulator connected to the second terminal; The cathode terminal of the variable shunt regulator is connected to the third terminal. The conversion circuit according to claim 1 or 2.

4. the regulator comprises an operational amplifier and a first NPN transistor; The positive input terminal of the operational amplifier is connected to the first terminal; The negative input terminal of the operational amplifier is connected to the reference voltage. an output terminal of the operational amplifier is connected to the base of the first transistor; The collector of the first transistor is connected to the third terminal, The emitter of the first transistor is connected to the second terminal. The conversion circuit according to claim 1 or 2.

5. the regulator comprises a first NPN transistor, a second NPN transistor, and a second resistor; The base of the first transistor is connected to the first terminal, the emitter of the first transistor is connected to the second terminal via the second resistor; the emitter of the first transistor is connected to the base of the second transistor; a collector of the first transistor is connected to a collector of the second transistor; The collector of the second transistor is connected to the third terminal, The emitter of the second transistor is connected to the second terminal. The conversion circuit according to claim 1 or 2.

6. the regulator comprises a first NPN transistor, a second NPN transistor, a third PNP transistor, a fourth NPN transistor, a second resistor, a third resistor, and a fourth resistor; The base of the first transistor is connected to the first terminal, the emitter of the first transistor is connected to the second terminal via the second resistor; the emitter of the first transistor is connected to the base of the second transistor; The collector of the first transistor is connected to the third terminal, The emitter of the second transistor is connected to the second terminal; a collector of the second transistor is connected to the third terminal via the third resistor; the collector of the second transistor is connected to the base of the third transistor; the emitter of the third transistor is connected to the third terminal; the collector of the third transistor is connected to the base of the fourth transistor; a collector of the third transistor is connected to the second terminal via the fourth resistor; The collector of the fourth transistor is connected to the third terminal, The emitter of the fourth transistor is connected to the second terminal. The conversion circuit according to claim 1 or 2.

7. the regulator comprises a first NPN transistor, a second NPN transistor, a third PNP transistor, a second resistor, and a third resistor; The base of the first transistor is connected to the first terminal, the emitter of the first transistor is connected to the second terminal via the second resistor; the emitter of the first transistor is connected to the base of the second transistor; The collector of the first transistor is connected to the third terminal, The emitter of the second transistor is connected to the second terminal; a collector of the second transistor is connected to the third terminal via the third resistor; the collector of the second transistor is connected to the base of the third transistor; the emitter of the third transistor is connected to the third terminal; The collector of the third transistor is connected to the second terminal. The conversion circuit according to claim 1 or 2.

8. The output impedance of the conversion circuit is 1 Ω or less. The conversion circuit according to claim 1 or 2.

9. a power supply resistor having one end connected to the third terminal and the other end connected to a power supply voltage; a capacitor having one end connected to the third terminal and the other end serving as an output end to a load side; and a capacitor having one end connected to the third terminal and the other end connected to the first terminal. The conversion circuit according to claim 1 or 2.

10. the regulator comprises a first field effect transistor, a second field effect transistor, and a second resistor; The gate of the first field effect transistor is connected to the first terminal, a source of the first field effect transistor is connected to the second terminal via the second resistor; the source of the first field effect transistor is connected to the gate of the second field effect transistor; a drain of the first field effect transistor is connected to a drain of the second field effect transistor; The drain of the second field effect transistor is connected to the third terminal; The source of the second field effect transistor is connected to the second terminal. The conversion circuit according to claim 1 or 2.

11. The regulator comprises an operational amplifier and a diode; The positive input terminal of the operational amplifier is connected to the first terminal; The negative input terminal of the operational amplifier is connected to the reference voltage. the output terminal of the operational amplifier is connected to the anode of the diode; The cathode of the diode is connected to the second terminal. The conversion circuit according to claim 1 or 2.

12. a positive power supply terminal of the operational amplifier is connected to the third terminal; The negative power supply terminal of the operational amplifier is connected to the second terminal. The conversion circuit according to claim 11.

13. The conversion circuit according to claim 1 or 2; and a sensor connected to the input.

14. The sensor is one of a condenser microphone, a piezoelectric sensor, a pressure sensor, an acceleration sensor, an optical sensor, and a quartz crystal oscillator.

14. The electronic circuit of claim 13.

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